The present invention relates generally to a process for evening out load fluctuation in an electricity supply network. The invention also relates to equipment for carrying out the process.
Thermal energy storage in thermal powr plants is an excellent means for dealing with medium-term fluctuations in the energy demand of the consuming network.
Processes for evening out load fluctuations and equipment required for carrying out the processes are known (Article by Gilly and Beckmann, Spitzenlastdeckung durch thermische Energiespeicherung [Covering Peak Loads by Thermal Energy Storage], VDI-Berichte No. 236, 1975, page 125 to 131). In these known processes, the water which leaves the expansion vessel and is collected in an auxiliary storage vessel is returned to the main store during charging and is thus heated up by the charging steam taken from the main circuit. It is mentioned in the same publication, however, that in principle, the store can be charged from the feedwater circuit. This process which utilizes a separate peak-load turbine, is alleged to have the advantage that the peak-load turbine can be located separately and that, if the store is not charged from the feedwater circuit, the main circuit is almost free from intervention. However, the utilization of the storage capacity is relatively poor in these processes, unless the expansion is carried out in several stages, which requires complicated circuit arrangements.
Overloading the turbine of the power station is regarded as a further possible way of covering peak loads. This can be effected, for example, in such a way that a displacement store completely filled with water is arranged parallel to the feedwater heaters of the plant, which are heated by bled steam, the contents of the displacement store being fed to the steam generator when the load rises suddenly and steeply (Dubbles Taschenbuch fur den Maschinenbau [Handbook of Mechanical Engineering], volume 2, Springer-Verlag, 1961, page 452).
In this way, the bleed points of the turbine are relieved, enabling it to deliver a higher output. This increase in output is, however, limited.
A primary object of the present invention is to provide a process and equipment for carrying out the process, which exhibit the advantages of both the known possible methods of covering peak loads.
In a process of the type outlined above, this is achieved if that part of the stored medium which is not vaporized on expansion is returned in liquid form to the main circuit when the store is discharged and the steam bled from the main circuit to heat the low-pressure feed-heaters is throttled or shut off.
Equipment of the type initially set out is characterized by the fact that the expansion vessel is connected on the water side to the feedwater tank of the main circuit and that at least one condensate vessel, which on the downstream side leads into the low-pressure feed-heater installation of the main circuit, is provided for the condensate from the turbine.
The advantages of the invention are in particular that, with the store fully or partially charged, operation is rendered flexible and immediately adaptable, and a small or very large additional output is obtainable. The latter results from the simultaneous utilization of the liquid and vaporous part of the stored energy carrier.